<section> <date> 20. July 2002 </date>
<h2> ZZIP API Basics </h2>              The open/close API description.

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<section>
<h3> Basics </h3>

<P>
  The naming schem of functions in this library follow a simple rule: 
  if you see a function with a <code>zzip_</code> prefix followed by 
  compact name representing otherwise a C library or posix function then 
  it is a magic wrapper that can automagically handle both real 
  files/directories or zip-contained files. This includes:
</P>
<table cellpadding=10 width=100%><tr><td><table width=100% border=1>
  <tr><td width=50%> zzip_opendir   </td><td width=50%> opendir </td></tr>
  <tr><td width=50%> zzip_readdir   </td><td width=50%> readdir </td></tr>
  <tr><td width=50%> zzip_closedir  </td><td width=50%> closedir </td></tr>
  <tr><td width=50%> zzip_rewinddir </td><td width=50%> rewinddir </td></tr>
  <tr><td width=50%> zzip_telldir   </td><td width=50%> telldir </td></tr>
  <tr><td width=50%> zzip_seekdir   </td><td width=50%> seekdir </td></tr>
</table></td></tr></table>
<P>
  The ZZIP_DIR handle can wrap both a real directory or a zip-file. 
  Note that you can not open a virtual directory <em>within</em> a
  zip-file, the ZZIP_DIR is either a real DIR-handle of a real 
  directory or the reference of ZIP-file but never a DIR-handle
  within a ZIP-file - there is no such schema of a SUB-DIR handle
  implemented in this library. A ZZIP_DIR does actually represent
  the central directory of a ZIP-file, so that each file entry in 
  this ZZIP-DIR can possibly have a subpath prepended.
</P>

<P>
  This form of magic has historic reasons as originally the 
  magic wrappers of this library were not meant to wrap a complete
  subtree of a real file tree but only a single directory being
  wrapped with into a zip-file and placed instead. Later proposals
  and patches were coming in to support subtree wrapping by not
  only making a split between the dir-part and file-part but
  going recursivly up through all "/"-dirseparators of a filepath
  given to <code>zzip_open</code> and looking for zip-file there.
</P>

<P>
  To open a zip-file unconditionally one should be using their
  respective methods that would return a ZZIP_DIR handle being
  the representant memory instance of a ZIP-DIR, the central
  directory of a zip-file. From that ZZIP-DIR one can open a
  compressed file entry which will be returned as a ZZIP_FILE
  pointer.
</P>
<table cellpadding=10 width=100%><tr><td><table border=1 width=100%>
  <tr><td width=50%> zzip_dir_open  </td>
      <td width=50%> open a zip-file and parse the central directory 
                                              to a memory shadow</td></tr>
  <tr><td width=50%> zzip_dir_close  </td>
      <td width=50%> close a zip-file and free the memory shadow</td></tr>
  <tr><td width=50%> zzip_dir_fdopen  </td>
      <td width=50%> acquire the given posix-file and try to parse it
                                                  as a zip-file.</td></tr>
  <tr><td width=50%> zzip_dir_read  </td>
      <td width=50%> return the next info entry of a zip-file's central
                 directory - this would include a possible subpath </td></tr>
</table></td></tr></table>

<P>
  To unconditionally access a zipped-file (as the counter-part of a 
  zip-file's directory) you should be using the functions having a
  <code>zzip_file_</code> prefix which are the methods working on
  ZZIP_FILE pointers directly and assuming those are references of
  a zipped file with a ZZIP_DIR. 
</P>
<table cellpadding=10 width=100%><tr><td><table border=1 width=100%>
  <tr><td width=50%> zzip_file_open  </td>
      <td width=50%> open a file within a zip and prepare a zlib 
                     compressor for it - note the ZZIP_DIR argument,
                     multiple ZZIP_FILE's may share the same central
                     directory shadow.</td></tr>
  <tr><td width=50%> zzip_file_close  </td>
      <td width=50%> close the handle of zippedfile
                     and free zlib compressor of it</td></tr>
  <tr><td width=50%> zzip_file_read  </td>
      <td width=50%> decompress the next part of a compressed file
                     within a zip-file</td></tr>
</table></td></tr></table>
<P>
  From here it is only a short step to the magic wrappers for
  file-access - when being given a filepath to zzip_open then
  the filepath is checked first for being possibly a real file
  (we can often do that by a <code>stat</code> call) and if there is
  a real file under that name then the returned ZZIP_FILE is
  nothing more than a wrapper around a file-descriptor of the
  underlying operating system. Any other calls like zzip_read
  will see the realfd-flag in the ZZIP_FILE and forward the 
  execution to the read() function of the underlying operating system.
</P>

<P>
  However if that fails then the filepath is cut at last directory
  separator, i.e. a filepath of "this/test/README" is cut into the
  dir-part "this/test" and a file-part "README". Then the possible
  zip-extensions are attached (".zip" and ".ZIP") and we check if
  there is a real file under that name. If a file "this/test.zip"
  does exist then it is given to zzip_dir_open which will create
  a ZZIP_DIR instance of it, and when that was successul (so it
  was in zip-format) then we call zzip_file_open which will see
  two arguments - the just opened ZZIP_DIR and the file-part. The
  resulting ZZIP_FILE has its own copy of a ZZIP_DIR, so if you
  open multiple files from the same zip-file than you will also
  have multiple in-memory copies of the zip's central directory
  whereas otherwise multiple ZZIP_FILE's may share a common
  ZZIP_DIR when being opened with zzip_file_open directly - the
  zzip_file_open's first argument is the ZZIP_DIR and the second
  one the file-part to be looked up within that zip-directory.
</P>

<table cellpadding=10 width=100%><tr><td><table border=1 width=100%>
  <tr><td width=50%> zzip_open  </td>
      <td width=50%> try the file-path as a real-file, and if not
                     there, look for the existence of ZZIP_DIR by
                     applying extensions, and open the file 
                     contained within that one.</td></tr>
  <tr><td width=50%> zzip_close  </td>
      <td width=50%> if the ZZIP_FILE wraps a real-file, then call
                     read(), otherwise call zzip_file_read() </td></tr>
  <tr><td width=50%> zzip_close  </td>
      <td width=50%> if the ZZIP_FILE wraps a real-file, then call
                     close(), otherwise call zzip_file_close() </td></tr>
</table></td></tr></table>

<P>
  Up to here we have the original functionality of the zziplib
  when I (Guido Draheim) created the magic functions around the work from 
  Tomi Ollila who wrote the routines to read and decompress files from
  a zip archive - unlike other libraries it was quite readable and
  intelligible source code (after many changes there is not much
  left of the original zip08x source code but that's another story).
  Later however some request and proposals and patches were coming in.
</P>

<P>
  Among the first extensions was the recursive zzip_open magic. In
  the first instance, the library did just do as described above:
  a file-path of "this/test/README" might be a zip-file known as
  "this/test.zip" containing a compressed file "README". But if 
  there is neither a real file "this/test/README" and no real
  zip-file "this/test.zip" then the call would have failed but
  know the zzip_open call will recursivly check the parent
  directories - so it can now find a zip-file "this.zip" which
  contains a file-part "test/README". 
</P>

<P>
  This dissolves the original meaning of a ZZIP_DIR and it has lead 
  to some confusion later on - you can not create a DIRENT-like handle
  for "this/test/" being within a "test.zip" file. And actually, I did
  never see a reason to implement it so far (open "this.zip" and set
  an initial subpath of "test" and let zzip_readdir skip all entries
  that do not start with "test/"). This is left for excercie ;-)
</P>
</section></section>
